This research was focused on the understanding of the biodegradability of synthetic anionic detergent powder available in Sri Lankan market. Eight different types of synthetic detergent powders were selected. LAS contents of the selected products were measured according to ASTM: D 3049-89 standard. The biodegradability was measured as the reduction percentage of LAS initially present, within a specific period. The phosphate content in the detergents were measured by SLS: 760, 1986 method and the pH of the media also was obtained to find any relationship between these parameters. The results found that the biodegradability of LAS in detergent powder is ranged between 24%-79%. This study found that the biodegradability of anionic surfactants highly depend on the phosphate content of the product. According to SLS 760:1986, minimum LAS %which has to be maintained in the Sri Lankan synthetic detergent and the existing legislations for the manufacturing, marketing and consuming of detergent products should have modified for the health and safety environment. Therefore further studies need to be conducted to determine the maximum allowable level of phosphates lead to the highest level of biodegradability.